The mucosal surfaces of the body are the portal of entry for many pathogenic micro- organisms yet most licensed vaccines are delivered parenterally and are ineffective at inducing mucosal immune responses. In addition, exposure of mucous membranes to most dietary and environmental antigens along with commensal micro-organisms leads to a state of immune tolerance rather than immunity. Thus non-living mucosal vaccines must employ adjuvants and be targeted to the immune inductive sites associated with mucous membranes. The most powerful mucosal adjuvant known is cholera toxin, but adverse side effects preclude the use of holotoxin cholera toxin in humans. We seek in this application to develop and understand the mechanisms behind a novel strategy for intranasal vaccination against pathogenic micro-organisms. This strategy will develop a vaccine immunogen which contains three components: (1) the enzymatically active CTA1 domain of cholera toxin as a safe and effective adjuvant, (2) a single chain variable region antibody fragment (scFv) which will target the vaccine to nasal passage and nasal associated lymphoid tissue (NALT) dendritic cells, and (3) an interchangeable polypeptide which can be selected to provide specific immunity versus targeted pathogens. We will evaluate this novel immunogen in mice employing both the model antigens Ovalbumin and ovalbumin peptides and two different classes of pathogens: a respiratory virus, Sendai virus and the gastric pathogen, Helicobacter pylori. These studies may lead both to an enhanced understanding of the role of subsets of dendritic cells in initiating mucosal immune responses, as well as a practical approach for achieving mucosal immune responses and avoiding mucosal tolerance. This application seeks to develop a novel way to immunize against micro-organisms which invade mucous membranes to cause disease. It will develop a new class of intranasal vaccines which combine antigens, a substance to enhance immune responses (an adjuvant) and a way to direct the vaccine to the tissues where an immune response to the vaccine is initiated.